1. Field of the Invention
The present invention relates to a surface acoustic wave device, and a process for fabricating the same.
2. Description of the Related Art
Generally, a surface acoustic wave device such as a surface acoustic wave (SAW) filter has a comb transducer comprised of an electrode pair on a transmitting side (simply called as “transmitting electrode”) and an electrode pair on a receiving side (simply called as “receiving electrode”) on a surface of a piezoelectric substrate. The transmitting electrode and the receiving electrode each has a pair of electrodes constructed such that an anode and a cathode intersect with each other. A surface acoustic wave excited by the transmitting electrode is propagated over the surface of the piezoelectric substrate, and is received by the receiving electrode for output.
In the piezoelectric substrate constituting the surface acoustic wave device, there is a wave other than the surface acoustic wave which is propagated from the transmitting electrode to the receiving electrode. Such an unnecessary, wave is propagated through the interior of the piezoelectric substrate, reflected on a back surface of the substrate, and is detected as an unnecessary wave signal. The unnecessary wave signal may adversely affect device characteristics if being received by the receiving electrode. In an attempt to eliminate the drawback, Japanese Unexamined Patent Publication No. 56-132806 discloses a technique in which plural grooves extending in a direction intersecting with the propagating direction of a surface acoustic wave are formed in a back surface of a piezoelectric substrate to vary the reflecting directions of the unnecessary wave on the back surface of the substrate for the purpose of reducing the unnecessary wave signal and suppressing adverse effects of the unnecessary wave signal.
Since the grooves for reducing the unnecessary wave signal are generally formed by a diamond cutter or a router, the grooves have a linear configuration and are formed equidistantly spaced apart from each other. Therefore, the reflecting conditions of the unnecessary wave to the respective grooves are identical to each other, which makes it difficult to provide advanced measures for reducing the unnecessary wave signal.